The long-term goal of this research is to better understand the factors determining the tumorigenic state of a cell and the relationship of these factors to the regulatory mechanisms responsible for the development and maintenance of the differentiated state. The experiments described here are designed to determine the relative role of nuclear and extranuclear factors in these regulatory events. Two teratocarcinoma-derived cell lines are being used in these studies: (1)\an embryonal carcinoma cell line (PCC3) which is (a)\pseudodiploid, (b)\multipotential, (c)\tumorigenic and (d)\expresses the SSEA-1 cell surface antigen and high levels of alkaline phosphatase activity; and (2)\a differentiated cell line (B2B2B1C14), isolated in this laboratory, which can be induced to differentiate into muscle and which is (a)\pseudodiploid, (b)\nontumorigenic and (c)\does not express the SSEA-1 cell surface antigen or significant levels of alkaline phosphatase activity. Somatic cell hybrids have been prepared between these two cell lines. Morphologically, these hybrids resemble the differentiated B2B2B1C14 cells and do not express the SSEA-1 cell-surface antigen. Alkaline phosphatase activity is reduced in these hybrids, but is not completely extinguished. The tumorigenic potential of these hybrids is currently being investigated, as well as their ability to differentiate into muscle. Next, cybrids were prepared by fusion of cytoplasts (enucleated cells), derived from a tetraploid PCC3 line, with B2B2B1C14 cells. Morphologically, these cybrids resemble the B2B2B1C14 cells--their further characterization is underway. Future plans include characterizing cybrids prepared by fusion of B2B2B1C14 cytoplasts with PCC3 cells and recombinant cells formed by the fusion of cytoplasts derived from one cell line with karyoplasts (nuclei surrounded by a small rim of cytoplasm) from the second cell line. It is hoped that these experiments will provide insight into (a)\the complexity of the regulatory network, (b)\the nuclear versus extranuclear location of various regulatory factors and (c)\the nature of the interaction between the regulatory factors controlling the differentiated and tumorigenic state of the cell.